This invention relates to apparatus for multiplexing and demultiplexing a plurality of various rate subchannels onto a fixed rate channel and more particularly to apparatus that is adaptive to different combinations of the subchannel and fixed channel rates.
In my co-pending patent application, Ser. No. 724,199, filed Apr. 17, 1985 now U.S. Pat. No. 4,617,658, entitled "Frame Arrangement for Multiplexing a Plurality of Subchannels onto a Fixed Rate Channel," I describe a framing structure which consists of j sets of i-tuples for ij bits per frame, the parameters i and j being mathematically determined as a function of the rates of the subchannels and the rate of the fixed channel. In j-1 of the i-tuples, i-1 bits are used for information and one bit at either end of the i-tulpes is set ONE (or ZERO). In one of the i-tuples, all i bits are set ZERO (or ONE). Framing is detected by monitoring for i successive ZEROes (or ONEs) followed or preceded by a ONE (or ZERO) which cannot occur elsewhere in the frame regardless of the data pattern. In the remaining (i-1)(j-1) bit positions in the frame, an integral number of information bits from each subchannel are distributed so that the required rate for each subchannel is provided.
In my aforenoted patent application, I describe in detail a multiplexer and demultiplexer which can multiplex and demultiplex, respectively, any one combination of subchannel rates using this frame structure once the values of i and j are calculated and bit assignments made within the frame. As digital links connected directly to users proliferate, flexible multiplexing and demultiplexing equipment that can be adapted on a line to line basis to meet each individual user's data needs is needed to permit maximum bandwidth utilization. Furthermore, equipment that can provide different rate mixtures on one line is desirable to provide the user with the flexibility to rearrange his mixture of data channels.